Diaphragm for electro-accoustic transducer

ABSTRACT

A diaphragm for electro-acoustic transducers, especially a diaphragm for speakers, and a film for the diaphragm excellent in the formability and the durability in high-output operation are obtained. A diaphragm for electro-acoustic transducers formed of a film that contains a polybiphenyl ether sulfone resin (A) having a specific repetitive unit or contains it and a crystalline resin (B) such as polyaryl ketone resin; and a film for use for the diaphragm.

CROSS-REFERENCE TO PRIOR RELATED APPLICATIONS

This is a U.S. National Phase application under 35 U.S.C. §371 ofInternational Application No. PCT/JP2007/050806, filed on Jan. 19, 2007,and claims benefit of Japanese Patent Application No. 2006-291149, filedon Oct. 26, 2006; Japanese Patent Application No. 2006-312866, filed onNov. 20, 2006; and Japanese Patent Application No. 2006-014107, filed onJan. 23, 2006. The applications are incorporated herein by reference.The International Application was published in Japanese on Jul. 26, 2007as WO 2007/083751 under PCT Article 221(2).

FIELD OF THE INVENTION

The present invention relates to a diaphragm for electro-acoustictransducers used in various acoustic instruments, and to a film for usefor it.

BACKGROUND

With the popularization of small electronics (for example, mobiletelephone, PDA, laptop computer, DVD, liquid-crystal TV, digital stillcamera, mobile music machinery, etc.), there is an increasing demand forsmall-sized electro-acoustic transducers, such as small-sized speakers(generally called microspeakers), small-sized receivers and furthermicrophones, earphones and others used in those electronics.

In general, a diaphragm for speakers is required to have a low densityso as to maintain the acoustic radiation sound pressure level, to havehigh rigidity for inhibiting strain so as to increase the allowableinput resistance, and additionally to have a large specific modulus ofelasticity so as to broaden the reproduction frequency band region, andto have a large internal loss for suppressing the divided vibration ofthe diaphragm so as to flatten the frequency characteristics. In usenear a speaker driving source, voice coil, or in use in in-vehiclespeakers, the diaphragm may be exposed to high temperature for a longperiod of time, and therefore it must have heat resistance fullybearable to such use conditions.

On the other hand, with the recent background of mobile or ubiquitoussociety or music source digitalization, various small electronics aremade to have higher function and higher performance. Even in thespeakers to be used in these, for example, in the speakers in mobiletelephones, the input-output resistance level required for the diaphragmis being improved to be at least from 0.5 to 0.6 W or so (at present,the uppermost limit is 1.2 W or so) for high-output models, as comparedwith popular models with 0.3 W or so. At present, there are many typesof models with from 0.6 to 0.8 W or so, and the ratio of models withmore than 1.0 W is low.

Regarding diaphragms for speakers, for example, Patent ReferencesJP-A-60-139099, JP-A-59-63897, and JP-A-2002-291092 disclose a diaphragmfor speakers, formed of a film of an aromatic polysulfone resin,concretely a polyether sulfone resin. These patent references disclosethat when a film of a polyether sulfone resin is used, the formability,the heat resistance and the acoustic characteristics of the diaphragmfor speakers are excellent. However, the diaphragm for speakersdescribed in these patent references is problematic in that itsdurability in high-output operation is insufficient and the diaphragmmay be often cracked or broken. In these patent references, nothing isdescribed or investigated relating to the structure of an aromaticpolysulfone resin, in particular to a diaphragm for speakers formed of afilm of an aromatic polysulfone resin having a specific repetitive unitand the durability thereof in high-output operation.

Japanese Patent JP-A-58-222699 discloses a diaphragm for speakers,formed of an aromatic polyether ketone resin, concretely apolyether-ether ketone resin. This patent reference says that themodulus of elasticity of the film of a polyether-ether ketone resin is30,000 kg/cm² (about 3000 MPa) and is high, and therefore the film isexcellent in high-pitched tone reproduction. However, this patentreference has no description of microspeakers and low-pitched tonereproduction with microspeakers, or has neither description norinvestigation of the durability in high-output operation of a diaphragmformed of a mixture of an aromatic polyether ketone resin and any otherresin and of the formability of the diaphragm.

On the other hand, as a diaphragm for speakers excellent in thedurability in high-output operation, used is a biaxially-stretchedthermally-fixed film of a polyethylene naphthalate resin (PEN) film or apolyphenylene sulfide resin (PPS) film. However, these films arecrystalline and their rigidity is too high, and therefore, their minimumresonance frequency (f₀: f zero) is high and their acousticcharacteristics are insufficient, for example, their low-pitched tonereproducibility is poor, and in particular, are problematic in thattheir formability into diaphragms (by press forming or vacuum forming)and their forming cycle are inferior to amorphous resins(polyetherimide, etc.) having a high glass transition temperature (Tg).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a diaphragm forelectro-acoustic transducers excellent in the formability and thedurability in high-output operation, and to provide a film for use inthe diaphragm.

Specifically, the present invention relates to the following:

(1) A diaphragm for electro-acoustic transducers, formed of a film, thefilm contains a polybiphenyl ether sulfone resin (A) having a repetitiveunit of the following structural formula (I):

wherein R₁ to R₄ each represent —O—, —SO₂—, —S— or —C═O, but at leastone of R₁ to R₄ is —SO₂— and at least one of R₁ to R₄ is —O—; whereinAr₁, Ar₂ and Ar₃ each represent an arylene group having from 6 to 24carbon atoms; and wherein a and b is 0 or 1;

(2) A diaphragm for electro-acoustic transducers, formed of a film, thefilm contains a polybiphenyl ether sulfone resin (A) having a repetitiveunit of the above structural formula (I), and a crystalline resin (B);and

(3) A film for use as the diaphragm for electro-acoustic transducers ofthe above (1) or (2).

According to the present invention, there are provided a diaphragm forelectro-acoustic transducers excellent in the formability and thedurability in high-output operation, and a film for diaphragms for usefor it.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in detail as follows.

“Main ingredient” in this specification means the ingredient containedmost abundantly, and its content is generally at least 50% by mass,preferably at least 80% by mass.

The diaphragm for electro-acoustic transducers of the present inventionincludes a filmcontaining a polybiphenyl ether sulfone resin (A). Inthis, the polybiphenyl ether sulfone resin is a thermoplastic resincontaining an aromatic nucleus bond, a sulfone bond, an ether bond and abiphenyl bond in its structural unit, and is an aromatic polysulfoneresin having a repetitive unit of the following structural formula (I):

In the above formula, R₁ to R₄ each represent —O—, —SO₂—, —S— or —C═O,but preferably —O— or —SO₂— from the viewpoint of the thermal stabilityand the forming workability. However, at least one of R₁ to R₄ is —SO₂—and at least one of R₁ to R₄ is —O—. Ar₁, Ar₂ and Ar₃ each represent anarylene group having from 6 to 24 carbon atoms, but preferably aphenylene group or a biphenylene group from the viewpoint of the heatresistance and the rigidity. a and b is 0 or 1.

In general, with the increase in the concentration of the biphenyl orbiphenylene group in the polybiphenyl ether sulfone resin (A), thecharacteristics such as the impact resistance of the polymer may bebetter. From this viewpoint, in the repetitive unit of the structuralformula (I), the arylene groups Ar₁, Ar₂ and Ar₃ are preferably in anamount of at least 50 mol % each, more preferably at least 75 mol %each; and preferably, they each are a biphenylene group such as ap-biphenylene group. Containing a biphenyl bond as the indispensableconstitutive unit, the resin may exhibit the excellent durability inhigh-output operation. The number of the repetitive units of thestructural formula (I) may be generally an integer of from 1 to 100, butpreferably from 20 to 50 from the viewpoint of securing the mechanicalproperties.

In this, the polybiphenyl ether sulfone resin having a repetitive unitof the structural formula (I) may have various combinations of therepetitive units, but in the present invention, the resin has a glasstransition temperature (Tg) of preferably from 150 to 320° C., morepreferably from 160 to 300° C., even more preferably from 180 to 250° C.When the glass transition temperature (Tg) of the resin is not lowerthan the above-mentioned lowermost limit, then it is favorable since thediaphragm may have sufficient heat resistance even when used near aspeaker driving source, voice coil or in in-vehicle speakers. On theother hand, when the temperature is not higher than the above-mentioneduppermost limit, then it is favorable since the diaphragm may be formed(by press forming or by vacuum forming) at a relatively low temperature.

In the present invention, in particular, a polyphenyl sulfone resinhaving a repetitive unit of the following structural formula (II) andhaving a glass transition temperature (Tg) of 220° C. is preferably usedas the polybiphenyl ether sulfone resin (A), from the viewpoint of theprocessability in film formation, and the workability, the heatresistance, the acoustic characteristics and the durability inhigh-output operation of the diaphragm. Concretely, it is commerciallyavailable as a trade name “Radel R” from Solvay Advanced Polymers.

The production method for the polybiphenyl ether sulfone resin (A) foruse in the present invention is not specifically defined, and knownmethods are all employable. For example, these are described in detailin the specifications of U.S. Pat. Nos. 3,634,355, 4,008,203, 4,108,837,4,175,175, etc. Commercially-available resins may be used directly asthey are. One or more different types of polybiphenyl ether sulfoneresins may be used either singly or as suitably combined.

The diaphragm for electro-acoustic transducers of the present inventionmay be formed of a film that contains the above-mentioned polybiphenylether sulfone resin (A); and from the viewpoint of the workability, theacoustic characteristics and the durability in high-output operation ofthe diaphragm, the resin composition to constitute the film preferablycontains the polybiphenyl ether sulfone resin (A) in an amount of atleast 50% by mass, more preferably at least 60% by mass, even morepreferably at least 80% by mass.

If desired, any other resin may be mixed in the resin composition toconstitute the film. In case of mixing it, the blend ratio by mass ispreferably polybiphenyl ether sulfone resin (A)/other resin=(1 to99)/(99 to 1), more preferably (30 to 90)/(70 to 10), even morepreferably (50 to 80)/(50 to 20), from the viewpoint of the workability,the acoustic characteristics and the durability in high-output operationof the diaphragm.

The other resin may include, for example, polyolefin resin, polyamideresin, polyester resin, syndiotactic polystyrene resin, polyurethaneresin, polysulfone resin, polyether sulfone resin, polyether ketoneresin, polyether-ether ketone resin, polyarylate resin, polyamideimideresin, polycarbonate resin, modified polyphenylene ether resin,polyetherimide resin, thermoplastic polyimide resin, polyether-nitrileresin, liquid-crystal polymer and thermoplastic elastomer; but in thepresent invention, from the viewpoint of the compatibility with thepolybiphenyl ether sulfone resin and the processability in filmformation, preferably used are polyether ketone resin, polyether-etherketone resin and polyetherimide resin, and more preferred ispolyether-ether ketone resin. One or more such other additional resinsmay be used herein, either singly or as suitably combined.

The diaphragm for electro-acoustic transducers of the present inventionis formed of a film that contains a polybiphenyl ether sulfone resin (A)and, as the other resin, a crystalline resin (B).

The polybiphenyl ether sulfone resin (A) is as described in the above.

The crystalline resin (B) is a resin that has a crystal melting peaktemperature (Tm) in differential scanning calorimetry, and for example,it includes polyolefin resin, polyamide resin, polyester resin,syndiotactic polystyrene resin, polyphenylene sulfide resin, polyketoneresin, polyaryl ketone resin, thermoplastic polyimide resin,polyether-nitrile resin; and one or more of these may be used eithersingly or as suitably combined.

Preferably, the crystal melting peak temperature (Tm) of the crystallineresin (B) is from 260 to 380° C., more preferably from 280 to 380° C.When the crystal melting peak temperature is not lower than 260° C.,then the heat resistance of the diaphragm for electro-acoustictransducers of the present invention may be improved, and, for example,the heat resistance in the reflow step may be secured. On the otherhand, when the crystal melting peak temperature is not higher than 380°C., then it is favorable since, for example, ordinary equipment may beused in melt forming into films and the films may be worked atrelatively low temperatures (the uppermost temperature of 430° C.).

Further, the crystal melting peak temperature (Tm) of the crystallineresin (B) and the glass transition temperature (Tg) of the polybiphenylether sulfone resin (A) are preferably in a relation of Tg<Tm, but morepreferably, Tm is higher by at least 30° C. than Tg. When the relationis satisfied, the film may be prevented from drawing down even thoughthere occurs a film temperature distribution within a temperature rangenot lower than the glass transition temperature (Tg) of the polybiphenylether sulfone resin (A) while the film is worked into a diaphragm byhot-press forming, and in addition, the stress-strain curve in theworking temperature range may be improved, and as a result, diaphragmsof good thickness accuracy may be fabricated.

In the present invention, polyaryl ketone resin is favorably used,having good compatibility with the polybiphenyl ether sulfone resin (A),having a forming and processing temperature range near to that of theresin (A) and having excellent heat resistance and mechanicalcharacteristics. The polyaryl ketone resin is a thermoplastic resincontaining an aromatic nucleus bond, an ether bond and a ketone bond inits structural unit; and its typical examples are polyether ketoneresin, polyether-ether ketone resin and polyether ketone ketone resinand others. In the present invention, favorably used is apolyether-ether ketone resin having a repetitive unit of the followingstructural formula (III), as having good compatibility (miscibility)with the polybiphenyl ether sulfone resin (A), having a forming andprocessing temperature range near to that of the resin (A) and havingexcellent heat resistance and mechanical characteristics, and from theviewpoint of the processability in film formation, and the workability,the heat resistance, the acoustic characteristics and the durability inhigh-output operation of the diaphragm.

The number of the repetitive units of the structural formula (III) maybe generally an integer of from 1 to 150, but preferably from 30 to 70from the viewpoint of securing the mechanical properties and of themelt-kneading/forming processability.

Concretely, they are commercially available from VICTREX as trade namesVICTREX PEEK “151G”, “381G”, “450G”; from DEGUSSA as trade namesVESTAKEEP “2000G”, “3001G”, “4000G”; from Solvay Advanced Polymers astrade names Keta Spire PEEK “KT-820NT”, “KT-880NT”; and from GhardaChemicals as trade names GATONE PEEK “5300”, “5400”, “5600” and others.

In the present invention, the blend ratio by mass of the above-mentionedpolybiphenyl ether sulfone resin (A) to the crystalline resin (B) ispreferably polybiphenyl ether sulfone resin (A)/crystalline resin(B)=(95 to 50)/(5 to 50). The blend ratio by mass falling within therange is favorable since, in general, when the resin composition isformed into a diaphragm by thermal press forming and the like in orderthat the amorphous resin, polybiphenyl ether sulfone resin (A) forms thematrix (sea) of the film, the workability and the working cycle aregood, and in addition, the adhesiveness to voice coils and housings withvarious adhesives (e.g., UV-curable adhesives such as acrylic or epoxyadhesives or solvent-diluting type adhesives) and organic solvents isalso good. Further, the crystalline resin (B) improves the heatresistance and the solvent resistance, and when the resin composition isformed into a diaphragm by thermal press forming and the like, thestress-strain curve within the working temperature range may also beimproved and, as a result, diaphragms of good thickness accuracy andgood deep drawability may be favorably fabricated. From these, in thepresent invention, the blend ratio by mass of the polybiphenyl ethersulfone resin (A) to the crystalline resin (B) is, as (A)/(B),preferably (95 to 55)/(5 to 45), more preferably (90 to 60)/(10 to 40);and even more preferably (A)/(B) is (85 to 65)/(15 to 35).

For the above-mentioned diaphragm for electro-acoustic transducers,preferably used is the film that contains, as the main ingredients, theabove-mentioned polybiphenyl ether sulfone resin (A) and the crystallineresin (B); and, if desired, any other resin may be mixed in the resincomposition to constitute the film in an amount of at most 30% by mass,preferably at most 20% by mass.

The other resin may include polyurethane resin, polysulfone resin,polyether sulfone resin, polyarylate resin, polycarbonate resin,modified polyphenylene ether resin, polyetherimide resin, thermoplasticpolyimide resin, liquid-crystal polymer and thermoplastic elastomer andthe like; but in the present invention, from the viewpoint of thecompatibility with the main ingredient resin and the processability infilm formation, preferably used are polysulfone resin and polyetherimideresin. One or more such other additional resins may be used herein,either singly or as suitably combined.

Further, filler and various additives, for example, heat stabilizer, UVabsorbent, light stabilizer, nucleating agent, colorant, lubricant andflame retardant may be suitably incorporated in the resin composition toconstitute the polybiphenyl ether sulfone resin-containing film.

The film for use in forming the diaphragm for electro-acoustictransducers of the present invention and its production methods aredescribed below. First, for the film formation method, any known methodis employable, including, for example, an extrusion casting method witha T-die, a calendering method or a flow casting method. An extrusioncasting method with a T-die is favorably employed from the viewpoint ofthe film producibility. The forming temperature in the extrusion castingmethod with a T-die may be suitably controlled depending on the flowcharacteristics and the film formability of the composition to be used,but may be generally from approximately 300° C. to 430° C. Any ofsingle-screw extruders, twin-screw extruders, kneaders and mixers andthe like generally used may be used herein. Preferred are twin-screwextruders and more preferred are co-rotating twin-screw extruders fromthe viewpoint of the uniform dispersibility of the mixed resincomposition and of the stability of the properties of the obtained film.

For the diaphragm for electro-acoustic transducers, especially for thediaphragm for speakers, the mean thickness may be from 5 to 150 μm,generally from approximately 8 to 100 μm. The film thickness accuracy(%) ([(film thickness−mean thickness)/(mean thickness)]×100) has someinfluence on the acoustic properties such as the reproduction frequencyband region and the frequency characteristics, and is thereforepreferably within ±10%, more preferably within ±8%, even more preferablywithin ±5%. Preferably, the film formation is so controlled that theanisotropy of the physical properties of the film in the machinedirection (MD) from the extruder and in the transverse direction (TD) isas small as possible.

Also preferably, the tensile modulus of elasticity of the film is from1000 MPa to less than 3000 MPa. When the tensile modulus of elasticityis at least 1000 MPa, then the film is favorably tough (stiff) enoughfor use as diaphragms for electro-acoustic transducers; while, on theother hand, when the tensile modulus of elasticity is less than 3000MPa, then it is also favorable since, for example for diaphragms formicrospeakers, even though the film having a thickness of from 20 to 40μm and having excellent handlability and durability in high-outputoperation is used, its minimum resonance frequency (f₀: f zero) issufficiently low, and the low-pitched tone reproducibility is secured toattain good sound quality. From these, in the present invention, theabove-mentioned tensile modulus of elasticity is more preferably from1000 MPa to less than 2500 MPa, even more preferably from 2000 MPa toless than 2500 MPa.

In this, for example, the polyethylene naphthalate resin (PEN) film hasa tensile modulus of elasticity of 6000 MPa or so, and therefore, fordiaphragms for microspeakers for mobile telephones and the like, thefilm must be considerably thinned for reducing its minimum resonancefrequency (f₀: f zero), and influence on the handling thereof and alsoduring the process of working into diaphragms due to static electricitybecomes large.

Thus obtained, the film is further worked into diaphragms forelectro-acoustic transducers. In this, a diaphragm for speakers isdescribed as one example. The working method is not specificallydefined. Taking its glass transition temperature and softeningtemperature into consideration, the film may be heated and worked into adome shape or a cone shape by press forming or vacuum forming. The shapeof the diaphragm is not specifically defined and may be any desired one.Any of circular, elliptical or oval shapes may be selected.

The film obtained in the present invention has a relative low tensilemodulus of elasticity, and therefore, especially when it is used fordiaphragms for small-sized electro-acoustic transducers, then it isfavorable since it may secure a low-pitched tone reproduction range andfor good sound quality. Regarding the size of the diaphragm, its maximumdiameter may be favorably at most 25 mm, preferably at most 20 mm andits lowermost limit may be generally 5 mm or so from the viewpoint ofreducing the size and the weight of the diaphragm. The maximum diametermeans the diameter of the diaphragm that is circular, and means themajor diameter of the diaphragm that is elliptical or oval.

In the present invention, as so described in the above, the shape of thediaphragm is not specifically defined and may be any desired one, andany of circular, elliptical or oval shapes may be selected. For example,in case where the diaphragm is desired to have deep drawability for therecess for holding a voice coil, as in Japanese patents JP-A-5-30592 and11-146487, it is desirable that the film to be used has a tensileelongation at break within the film-working temperature range of atleast 100%, preferably at least 200%, more preferably at least 300%. Theuppermost limit may be generally 600% or so. In this, the film having atensile elongation at break of at least 300% is especially favorablesince it may be stably worked into various shapes of diaphragms withlittle trouble of breakage.

The surface of the diaphragm may be suitably worked to have a groovewith a V-shaped cross-sectional profile, referred to as a tangentialedge. In this case, the mean thickness of the film is preferably at most40 μm, more preferably from 20 to 38 μm. This is because the filmthickness could be sufficiently secured and therefore the filmhandlability is good and the film workability per hour in press formingand the like and the working accuracy (shape reproducibility) arereadily improved. In addition, for controlling the workability and thedust repellency and also the acoustic characteristics of the diaphragm,the surface of the film or the shaped diaphragm may be further coatedwith an antistatic agent or various elastomer (e.g., urethane-type,silicone-type, hydrocarbon-type or fluorine-containing elastomer or thelike), or may be coated with metal by vapor deposition or sputtering, ormay be suitably processed for coloring (black, white or others).Further, the diaphragm may be suitably laminated with a metal such asaluminium or with any other film, or may be hybridized with a nonwovenfabric.

The diaphragm for electro-acoustic transducers of the present inventionis, when used as a diaphragm for speakers, for example, excellent in thedurability in high-output operation. For example, ordinary models ofmobile telephones have an output resistance level of 0.3 W or so; butthe diaphragm of the present invention is applicable to high-outputmodels with an output resistance level of from approximately 0.6 to 1.0W. In addition, since polybiphenyl ether sulfone resin is generally anamorphous highly heat-resistant resin, the film that contains thepolybiphenyl ether sulfone resin (A), and further the film that containsthe polybiphenyl ether sulfone resin (A) and the crystalline resin (B),especially the film that contains the above resin (A) or the resin (A)and the resin (B) as the main ingredients are excellent in the basicacoustic characteristics as diaphragms for speakers, especially asdiaphragms for microspeakers, and in addition, excellent in the heatresistance and the formability at the working into diaphragms.

As in the above, the diaphragm for electro-acoustic transducers of thepresent invention is favorably used as diaphragms for speakers from theviewpoint of the heat resistance, the acoustic characteristics and thedurability in high-output operation thereof; and regarding theapplication range of the diaphragm for electro-acoustic transducers ofthe present invention, it is applicable to all electro-acoustictransducers including speakers and in addition, receivers, microphonesand earphones. In particular, the diaphragm is favorable formicrospeakers of mobile telephones.

The present invention is described more concretely with reference to thefollowing Examples, by which, however, the present invention should notbe limited at all. Various data and evaluation of the films shown inthis specification are determined as follows. In this, the flowdirection of the film from extruder is referred to as the machinedirection, and the direction perpendicular to it is as the crossdirection.

(1) Glass Transition Temperature (Tg), Crystal Melting Peak Temperature(Tm):

Using Perkin Elmer's DSC-7, 10 mg of a sample is heated at a heatingrate of 10° C./min according to JIS K7121, and the data are obtainedfrom the thermogram.

(2) Film Specific Gravity:

The obtained film is analyzed according to JIS K7112 (method D).

(3) Tensile Modulus of Elasticity:

The obtained film is analyzed for the cross direction, according to JISK7127 at a temperature of 23° C.

(4) Tensile Elongation at Break (200° C.)

The obtained film is analyzed for the machine direction, according toJIS K7127 at a temperature of 200° C. and at a test speed of 200 mm/min.In addition, the results as evaluated according to the followingstandards are also shown.

-   (Excellent): The tensile elongation at break is at least 300%.-   (Good): The tensile elongation at break is from 100% to less than    300%.-   (Poor): The tensile elongation at break is less than 100%.

(5) Durability Evaluation:

The obtained film is heated at 230° C. and formed into a o16-mm circulardomed diaphragm having a tangential edge, according to press forming.Next, a microspeaker unit comprising a voice coil, a magnet, a frame anda damper is constructed. The obtained microspeaker is connected to theterminal of a durability tester (SIGMA Electronics' ST-2000B), and whilethe load thereto is changed in an EIA mode with white noise, thecondition of the diaphragm is evaluated.

Regarding the above evaluation, in Examples 1 and 2 and ComparativeExample 1, the condition of the diaphragm is evaluated according to thefollowing standards while the load thereto is changed on 3 levels of 0.3W (1.55 V), 0.7 W (2.37 V) and 1.0 W (2.83 V) in an EIA mode with whitenoise of the durability tester (SIGMA Electronics' ST-2000B) (number oftested samples: 5 sets).

-   (Good): In at least 4 sets, the diaphragm is neither cracked nor    broken in continuous input operation for 100 hours.-   (Fair): In at least 2 sets, the diaphragm is cracked or broken    within from 10 hours to less than 100 hours.    (Poor): In at least one set, the diaphragm is cracked or broken    within less than 10 hours.

In Examples 3 to 5 and Comparative Examples 1 and 2, the input load ischanged at an interval of 0.1 W from 0.3 W (1.55 V) to 0.8 W (2.53 V) inan EIA mode with white noise, and in continuous input operation for 100hours, the maximum input level (W) at which all the diaphragms of 5 setsare neither cracked nor broken is read. In addition, the results asevaluated according to the following standards are also shown.

(Good): The maximum input level is at least 0.6 W.

-   (Poor): The maximum input level is at most 0.5 W.

(6) Mean Thickness of Film:

The obtained film was measured at 20 points at regular intervals in thecross direction thereof, using a micrometer, and the data are averaged.

EXAMPLE 1

As a polybiphenyl ether sulfone resin, 100 parts by mass of polyphenylsulfone resin (Solvay Advanced Polymers' Radel R-5000, amorphous resinhaving Tg of 220° C.) (hereinafter this may be simply abbreviated asPPSU) was melt-kneaded, using a single-screw extruder having a diameterof 40 mm and equipped with a T-die, at a set temperature of 370° C., andrapidly cooled on a cast roll at 190° C. for film formation thereon togive a film having a mean thickness of 35.0 μm. The obtained film wasevaluated and the results are shown in Table 1.

EXAMPLE 2

A film having a mean thickness of 35.0 μm was obtained in the samemanner as in Example 1, for which, however, the resin composition toconstitute the film was changed from 100 parts by mass of PPSU to amixed resin composition of 50 parts by mass of PPSU and 50 parts by massof polyether-ether ketone resin (Victrex's PEEK450G, having Tg of 143°C. and Tm of 334° C.) (hereinafter this may be simply abbreviated asPEEK). The obtained film was evaluated and the results are shown inTable 1.

COMPARATIVE EXAMPLE 1

A film having a mean thickness of 35.0 μm was obtained in the samemanner as in Example 1, for which, however, the resin composition toconstitute the film was changed from 100 parts by mass of PPSU to 100parts by mass of polyether sulfone resin (Sumitomo Chemical'sSUMICAEXCEL PES4100G, amorphous resin having Tg of 223° C.) (hereinafterthis may be simply abbreviated as PES). The obtained film was evaluatedand the results are shown in Table 1.

TABLE 1 Comparative Example 1 Example 2 Example 1 PPSU (mas. pt.) 100 50PEEK (mas. pt.) 50 PES (mas. pt.) 100 Film specific gravity (—) 1.291.30 1.37 Tensile modulus of 2300 2850 2600 elasticity (MPa) Durability0.3 W Good Good Good evaluation 0.7 W Good Good Poor 1.0 W Fair Good —

From Table 1, it is confirmed that the diaphragms for speakers formed ofthe polybiphenyl ether sulfone resin-containing film of the presentinvention have good formability and are excellent in the durability inhigh-output operation (Example 1, Example 2). On the other hand, it isconfirmed that the diaphragm for speakers formed of the film of aconventional polyether sulfone resin not having a biphenyl bond is goodat the formability but its durability in high-output operation isinsufficient (Comparative Example 1).

EXAMPLE 3

85 parts by mass of PPSU as a polybiphenyl ether sulfone resin (A) and15 parts by mass of PEEK as a crystalline resin (B) were melt-kneaded ata set temperature of 370° C., using a single-screw extruder having adiameter of 40 mm and equipped with a T-die, and then rapidly cooled ona cast roll at 190° C. thereby producing a film having a mean thicknessof 35.0 μm. The obtained film was evaluated and the results are shown inTable 2.

EXAMPLE 4

A film having a mean thickness of 35.0 μm was obtained in the samemanner as in Example 3, for which, however, the resin composition toconstitute the film was changed to a mixed resin composition of 70 partsby mass of PPSU and 30 parts by mass of PEEK as in Table 2. The obtainedfilm was evaluated and the results are shown in Table 2.

EXAMPLE 5

A film having a mean thickness of 35.0 μm was obtained in the samemanner as in Example 3, for which, however, polyether-ether ketone resin(Victrex's PEEK-HTG22, having Tg of 162° C. and Tm of 378° C.)(hereinafter this may be simply abbreviated as PEK) was used in place ofPEEK as the crystalline resin (B) in Example 4, as in Table 2, and theset temperature in melt-kneading was changed to 390° C. The obtainedfilm was evaluated and the results are shown in Table 2.

COMPARATIVE EXAMPLE 2

A film having a mean thickness of 35.0 μm was obtained in the samemanner as in Example 3, for which, however, the resin composition toconstitute the film was changed from PPSU in Example 4 to PES, as inTable 2. The obtained film was evaluated and the results are shown inTable 2.

Also the film obtained in Comparative Example 1 was evaluated for itsdurability in the same manner as in Examples 3 to 5, and the results areshown in Table 2.

TABLE 2 Comparative Example Example 3 4 5 1 2 PPSU (mas. pt.) 85 70 70PES (mas. pt.) 100 70 PEEK (mas. pt.) 15 30 30 PEK (mas. pt.) 30 Filmspecific 1.29 1.29 1.30 1.37 1.33 gravity (—) Tensile modulus 2320 23502470 2600 2660 of elasticity (MPa) Durability (W) 0.7 0.8 0.8 0.5 0.4Good Good Good Poor Poor Tensile 358.2 464.9 421.1 93.1 168.4 elongationat Excellent Excellent Excellent Poor Good break (%) (200° C.)

From Table 2, it is confirmed that the diaphragms for speakers formed ofthe film containing, as the main ingredients, the polybiphenyl ethersulfone resin (A) and the crystalline resin (B) of the present inventionhave good formability and are excellent in the durability in high-outputoperation, and in addition, the tensile elongation at break thereofwithin the processing temperature range (200° C.) is large, and, forexample, they are also excellent in the deep drawability (Examples 3 to5). The tensile elongation at break at 200° C. of the film of PPSU alonewas 285.2%. On the other hand, it is confirmed that the diaphragms forspeakers formed of the film of a conventional polyether sulfone resinnot having a biphenyl bond (Comparative Example 1) or the filmcontaining the resin and PEEK (Comparative Example 2) are excellent inthe formability but their durability in high-output operation isinsufficient. The miscibility between PES and PEEK is inferior to themiscibility between PPSU and PEEK, and therefore it is confirmed that,in Comparative Example 2, even though PEEK was mixed in the composition,the durability of the diaphragm was rather lowered.

The diaphragm for electro-acoustic transducers of the present inventionis excellent in the formability and the durability in high-outputoperation, and is therefore usable as diaphragms for speakers used invarious small electronics (for example, mobile telephone, PDA, laptopcomputer, DVD, liquid-crystal TV, digital still camera, mobile musicmachinery, etc.), and also in electro-acoustic transducers such asreceivers, microphones and earphones.

Having described preferred embodiments of the invention, it is to beunderstood that the invention is not limited to those preciseembodiments, and that various changes and modifications may be effectedtherein by one skilled in the art without departing from the scope orspirit of the invention as defined in the appended claims.

1. A diaphragm for electro-acoustic transducers formed of a film thatcontains a polybiphenyl ether sulfone resin (A) having a repetitive unitof the following structural formula (1):

wherein R₁ to R₄ each represent —O—, —SO₂—, —S— or C═O, but at least oneof R₁ to R₄ is —SO₂— and at least one of R₁ to R₄ is —O—; Ar₁, Ar₂ andAr₃ each represent an arylene group having from 6 to 24 carbon atoms;and a and b each are any of 0 or 1, wherein the diaphragm consists ofthermoplastic resins.
 2. A diaphragm for electro-acoustic transducersformed of a film that contains a polybiphenyl ether sulfone resin (A)having a repetitive unit of the following structural formula (1):

wherein R₁ to R₄ each represent —O—, —SO₂—, —S— or C═O, but at least oneof R₁ to R₄ is —SO₂— and at least one of R₁ to R₄ is —O—; Ar₁, Ar₂ andAr₃ each represent an arylene group having from 6 to 24 carbon atoms;and a and b each are any of 0 or 1₁ wherein the film does not contain aflame retardant.